Network Working Group C. Allocchio
Request for Comments: 3191 GARR-Italy
Obsoletes: 2303 October 2001
Updates: 2846
Category: Standards Track
Minimal GSTN address format in Internet Mail
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
This memo describes a simple method of encoding Global Switched
Telephone Network (GSTN) addresses (commonly called "telephone
numbers") in the local-part of Internet email addresses, along with
an extension mechanism to allow encoding of additional standard
attributes needed for email gateways to GSTN-based services.
1. Introduction
As with all Internet mail addresses, the left-hand-side (local-part)
of an address generated according to this specification, is not to be
interpreted except by an MTA that handles messages for the domain
given in the right-hand-side.
Since the very first e-mail to GSTN services gateway appeared, a
number of different methods to specify a GSTN address as an e-mail
address have been used by implementors. Several objectives for this
methods have been identified, like to enable an e-mail user to access
GSTN services from his/her e-mail interface, to allow some kind of
"GSTN over e-mail service" transport (possibly reducing the costs of
GSTN long distance transmissions) while using the existing e-mail
infrastructure.
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RFC 3191 Minimal GSTN address format in Internet Mail October 2001
This memo describes the MINIMAL addressing method to encode GSTN
addresses into e-mail addresses and the standard extension mechanism
to allow definition of further standard elements. The opposite
problem, i.e., to allow a traditional numeric-only GSTN device user
to access the e-mail transport service, is not discussed here.
The IANA registration templates which MUST be used to register any
standard element defined according to this specification are given in
the "IANA Considerations" chapter (section 7 of this document).
All implementations supporting this GSTN over e-mail service MUST
support as a minimum the specification described in this document.
The generic complex case of converting the entirety of GTSN
addressing into e-mail is out of scope in this minimal specification.
1.1 Terminology and Syntax conventions
In this document the formal definitions are described using ABNF
syntax, as defined into [7]. This memo also uses some of the "CORE
DEFINITIONS" defined in "APPENDIX A - CORE" of that document. The
exact meaning of the capitalized words
"MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
"SHOULD NOT", "RECOMMENDED", "MAY", "OPTIONAL"
is defined in reference [6].
In this document the following new terms are also defined:
I-pstn device:
a device which has an Internet domain name and it is able to
communicate either directly or indirectly with the GSTN
network;
mta-I-pstn:
the Internet domain name which identifies uniquely an I-pstn
device over the Internet;
pstn-email:
the complete Internet e-mail address structure which is used to
transport a GSTN address over the Internet e-mail service.
2. Minimal GSTN address
The minimal specification of a GSTN address within an e-mail address
is as follows:
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RFC 3191 Minimal GSTN address format in Internet Mail October 2001
pstn-address = pstn-mbox [ qualif-type1 ]
pstn-mbox = service-selector "=" global-phone
service-selector = 1*( DIGIT / ALPHA / "-" )
; note that SP (space) is not allowed in
; service-selector.
; service-selector MUST be handled as a case
; INSENSITIVE string by implementations.
Other specifications adopting the "pstn-address" definition MUST
define and register with IANA a unique case insensitive
"service-selector" element to identify the specific messaging service
involved.
These specifications and registrations MUST also define which minimal
"qualif-type1" extensions, if any, MUST be supported for the
specified messaging service.
Implementations confirming to this minimal requirements specification
are allowed to ignore any other non-minimal extensions address
element which is present in the "pstn-address". However, conforming
implementations MUST preserve all "qualif-type1" address elements
they receive.
The generic "qualif-type1" element is defined as:
qualif-type1 = "/" keyword "=" string
keyword = 1*( DIGIT / ALPHA / "-" )
; note that SP (space) is not allowed in keyword
string = PCHAR
; note that printable characters are %x20-7E
As such, all "pstn-address" extension elements MUST be defined in the
"qualif-type1" form at the time of registration with IANA.
2.1 Minimal "global-phone" definition
The purpose of global-phone element is to represent standard E.164
numeric addresses [10] within a syntax for electronic mail addressing
that is compliant with standard e-mail specifications given in [1]
and [2].
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The minimal supported syntax for global-phone element is as follows:
global-phone = "+" 1*( DIGIT / written-sep )
written-sep = ( "-" / "." )
The use of other dialing schemes for GSTN numbers (like private
numbering plans or local dialing conventions) is also allowed.
However, this does not preclude nor remove the mandatory requirement
for support to the "global-phone" syntax within the minimal GSTN
address format.
Any other dialing schemes MUST NOT use the leading "+" defined here
between the "=" sign and the dialing string. The "+" sign is
strictly reserved for the standard "global-phone" syntax.
Note:
The specification of alternate dialing schemas is out of scope for
this minimal specification.
This document also permits the use of written-sep elements in order
to improve human readability of GSTN e-mail addresses. The
written-sep are elements which can be placed between dial elements
such as digits etc.
Implementors' note:
Use of the written-sep elements is allowed, but not recommended
for transmission. Any occurrences of written-sep elements in a
pstn-mbox MUST be ignored by all conformant implementations.
2.2 The minimal "pstn-address" examples
Some examples of minimal pstn-address are:
VOICE=+3940226338
FAX=+12027653000/T33S=6377
SMS=+33-1-88335215
Note:
these examples are given as illustrations only; they do not
necessarily represent valid pstn-addresses.
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RFC 3191 Minimal GSTN address format in Internet Mail October 20013. The e-mail address of the I-pstn device: mta-I-pstn
An "I-pstn device" has, among its characteristics, a unique Internet
domain name which identifies it on the Internet. Within Internet
mail, this is the Right Hand Side (RHS) part of the address, i.e.,
the part on the right of the "@" sign. For purposes of this document
we will call this "mta-I-pstn"
mta-I-pstn = domain
For "domain" strings used in SMTP transmissions, the string MUST
conform to the requirements of that standards <domain> specifications
[1], [3]. For "domain" strings used in message content headers, the
string MUST conform to the requirements of the relevant standards
[2], [3].
Note:
the use of "domain names" or "domain literals" is permitted in
addresses in both the SMTP envelope and message header fields.
4. The pstn-email
The complete structure used to transfer a minimal GSTN address over
the Internet e-mail transport system is called "pstn-email". This
object is a an e-mail address which conforms to [2] and [3]
"addr-spec" syntax, with structure refinements which allows the GSTN
number to be identified.
pstn-email = ["""] ["/"] pstn-address ["/"] ["""] "@" mta-I-pstn
Implementors' note:
The optional "/" characters can result from translations from
other transport gateways (such as some X.400 gateways) which have
included the "/" as an optional element. Implementations MUST
accept the optional slashes but SHOULD NOT generate them.
Gateways are allowed to strip them off when converting to Internet
mail addressing. The relevant standard [2], [3] define exactly
when the optional "quotes" characters surrounding the entire local
part (i.e., the part on the left of the "@" character into the
pstn-email) MUST be added.
4.1 Multiple subaddresses
There are some instances in GSTN applications where multiple
subaddresses are used. On the other hand in e-mail practice a
separate and unique e-mail address is always used for each recipient.
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RFC 3191 Minimal GSTN address format in Internet Mail October 2001
In the event a particular GSTN service requires multiple subaddresses
(in any form defined by the standard specification for that GSTN
service) that are associated with the same "pstn-mbox", then the use
of multiple "pstn-email" elements is REQUIRED.
Implementors' note:
The UA may accept multiple subaddress elements for the same
global-phone, but it MUST generate multiple "pstn-mbox" elements
when submitting the message to the MTA.
4.2 Some examples of minimal "pstn-email" addresses
Some examples of minimal pstn-email addresses follows:
VOICE=+3940226338@worldvoice.com
FAX=+1.202.7653000/T33S=6377@faxserv.org
/SMS=+33-1-88335215/@telecom.com
Note:
these examples are given as illustrations only; they do not
necessarily represent valid pstn-addresses.
5. Conclusions
This proposal creates a minimal standard encoding for GSTN addresses
within the global e-mail transport system. It also defines the
standard extension mechanism to be used to introduce new elements for
GSTN addresses.
The proposal is consistent with existing e-mail standards. Each
specific GSTN service using this proposal MUST define and register
with IANA its own "service-selector" specification and MUST define
and register the eventual other "qualif-type1" elements needed for
its specific application. An example of such an application is
contained in reference [13].
6. Security Considerations
This document specifies a means by which GSTN addresses can be
encoded into e-mail addresses. Since e-mail routing is determined by
Domain Name System (DNS) data, a successful attack to DNS could
disseminate tampered information, which causes e-mail messages to be
diverted via some MTA or Gateway where the security of the software
has been compromised.
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There are several means by which an attacker might be able to deliver
incorrect mail routing information to a client. These include: (a)
compromise of a DNS server, (b) generating a counterfeit response to
a client's DNS query, (c) returning incorrect "additional
information" in response to an unrelated query. Clients SHOULD
ensure that mail routing is based only on authoritative answers.
Once DNS Security mechanisms [5] become more widely deployed, clients
SHOULD employ those mechanisms to verify the authenticity and
integrity of mail routing records.
7. IANA Considerations
As the service-selector and qualif-type1 elements values are
extensible, they MUST be registered with IANA.
To register a service-selector or a qualif-type1 element, the
registration form templates given in 7.1 and 7.2 MUST be used. Any
new registration MUST fulfill the "Specification Required" criteria,
as defined in RFC 2434, section 2 [16]:
"Specification Required - Values and their meaning MUST be
documented in an RFC or other permanent and readily available
reference, in sufficient detail so that interoperability between
independent implementations is possible."
IANA MUST NOT accept registrations which are not supplemented by a
Specification as defined above and which are not fully specified
according to the template forms given in 7.1 and 7.2. In case of
need for further consultation about accepting a new registration,
IANA SHOULD refer to the Application Area Director to be directed to
the appropriate "expert" individual or IETF Working Group.
After successful registration, IANA should publish the registered new
element in the appropriate on-line IANA WEB site, and include it into
the updates of the "Assigned Numbers" RFC series.
This section (including 7.1 and 7.2) updates the ones contained in
[15].
7.1 IANA Registration form template for new values of GSTN address service-selector
To: IANA@iana.org
Subject: Registration of new values for the GSTN address
service-selector specifier "foo"
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RFC 3191 Minimal GSTN address format in Internet Mail October 2001
service-selector name:
foo
Description of Use:
foo - ("foo" is a fictional new service-selector used in this
template as an example, it is to be replaced with the new value
being registered. Include a short description of the use of the
new value here. This MUST include reference to Standard Track
RFCs and eventually to other Standard Bodies documents for the
complete description; the use of the value must be defined
completely enough for independent implementation).
Security Considerations:
(Any additional security considerations that may be introduced by
use of the new service-selector parameter should be defined here
or in the reference Standards Track RFCs)
Person & email address to contact for further information:
(fill in contact information)
INFORMATION TO THE SUBMITTER:
The accepted registrations will be listed in the "Assigned
Numbers" series of RFCs. The information in the registration form
is freely distributable.
7.2 IANA Registration form template for new values of GSTN address qualif-type1 keyword and value
To: IANA@iana.org
Subject: Registration of new values for the GSTN address
qualif-type1 element "bar"
qualif-type1 "keyword" name:
bar
qualif-type1 "value" ABNF definition:
abnf - ("abnf" MUST define the ABNF form of the qualif-type1
value. The ABNF specification MUST be self-contained, using as
basic elements the tokens given in specification [4]. To avoid
any duplication (when appropriate), it MUST also use any already
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RFC 3191 Minimal GSTN address format in Internet Mail October 2001
registered non-basic token from other qualif-type1 elements, i.e.,
it MUST use the same non-basic token name and then repeat its
identical ABNF definition from basic tokens.
Description of Use:
bar - ("bar" is a fictional description for a new qualif-type1
element used in this template as an example. It is to be replaced
by the real description of qualif-type1 element being registered.
Include a short description of the use of the new qualif-type1
here. This MUST include reference to Standards Track RFCs and
eventually to other Standard Bodies documents for the complete
description; the use of the value MUST be defined completely
enough for independent implementation.)
Use Restriction:
(If the new qualif-type1 elements is meaningful only for a
specific set of service-element, you MUST specify here the list of
allowed service-element types. If there is no restriction, then
specify the keyword "none")
Security Considerations:
(Any additional security considerations that may be introduced by
use of the new service-selector parameter should be defined here
or in the reference Standards Track RFCs)
Person & email address to contact for further information:
(fill in contact information)
INFORMATION TO THE SUBMITTER:
The accepted registrations will be listed in the "Assigned
Numbers" series of RFCs. The information in the registration form
is freely distributable.
8. Changes from RFC 2303 specification
Although there are no technical or major changes from RFC 2303
specification, this section briefly describes where updates and
clarifications were introduced:
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RFC 3191 Minimal GSTN address format in Internet Mail October 2001
- considering the case that telephony systems do not conform any
more to the "single/few" Public Operator paradigm, the old
definition "PSTN - Public Switched Telephone Network" was changed
into the more adequate "GSTN - Global Switched Telephone Network"
one. However, in order to remain consistent with the previous
specification, the ABNF variables names were not changed.
- it was made clear that "GSTN addresses" correspond, in common
language, to "telephone numbers" and that the "global-phone" is a
representation of E.164 numeric addresses;
- an explicit list of "new terms" with explanations was added to
section 1.1;
- the fact that any other specification adopting the "pstn-address"
definition MUST register with IANA the new "service-selector" and
"qualif-type1" elements was made explicit throughout the document;
the relevant mechanism to be used was added in section 7 "IANA
considerations" (including the IANA Registration form templates);
this is also consistent with RFC 2846;
- in section 2.1 the use and meaning of "written-sep" was clarified;
- in section 4., the quoting rules of the "pstn-address" and their
practical use was made explicit both in the definition of
pstn-email" and in the Implementors' note;
- section 4.1 was updated to clarify how to generate "pstn-email"
when more than one subaddress is used;
- the Author's Address was updated;
- the References list was updated to include RFC 2846 and RFC 2434.
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RFC 3191 Minimal GSTN address format in Internet Mail October 2001
Full Copyright Statement
Copyright (C) The Internet Society (2001). All Rights Reserved.
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